DETECTION OF SOLUBLE TYPE-II RECEPTOR IN THE PRESENCE OF ITS NATURAL LIGAND IL-1-BETA QUANTIFICATION BY SANDWICH ELISA

The type II interleukin-1 receptor (IL-1R II) is a newly described 60- 68 kDa protein expressed on monocytes, neutrophils, and lymphocytes. I t is hypothesized that a 45 kDa soluble form of the IL-1R II attenuate s the proinflammatory effects of IL-1 by preventing its binding to the type I IL-1 receptor. However, very little information exists regardi ng the detection of soluble IL-1R II. Specifically, there are no repor ts to date characterizing IL-IR II detection by enzyme-linked immunoas say in the presence of IL-1 beta or characterizing IL-1 beta detection in the presence of IL-1R II. This study addresses the detection and q uantitation of IL-1R II and IL-1 beta by a number of sandwich ELISA fo rmats and characterizes the sensitivity of detection in the presence o f competitive cytokines. We generated two distinct IL-1R II sandwich E LISAs that can detect receptor down to a level of 50 pg/ml. One, M22/R 2, detects only unbound IL-1R II and the other, M2/R2, detects both bo und and unbound IL-1R II. In this context, a 4:1 molar ratio of IL-1 b eta to IL-1R II interferes with the IL-1R II detection by the M22/R2 b ut not the M2/R2 ELISA. Conversely, IL-1R II at physiologically releva nt concentrations interferes with the detection of IL-1 beta by three distinct IL-1 beta ELISA formats. Taken together, these studies sugges t that when measuring samples that may contain both IL-1 beta and IL-1 R II, careful attention must be given to assay specificity.